In optical communication networks, it is often desirable to use modular electrical and/or optical components to reduce manufacturing costs. For example, it is common to use electro-optical assemblies to transmit and receive optical signals over optical fibers. A typical electro-optical assembly comprises various modular components combined in a package assembly. For example, a typical electro-optical assembly comprises a transmitter optical subassembly (TOSA), a receiver optical subassembly (ROSA), and an electronic subassembly. The TOSA generally comprises a light source for transmitting optical signals and control circuitry for modulating the light source according to an input digital data signal from the electronic subassembly. The TOSA also includes an optical lens for coupling the light signals from the light source of the TOSA to an optical fiber that may be connected to the TOSA housing. The ROSA generally comprises a photodiode for detecting optical signals and sensing circuitry for converting the optical signals to digital signals provided to the electronic subassembly. The TOSA and ROSA are typically formed in a subassembly having electrical connections for connecting to the electronic subassembly and plug-type receptacles for optically connecting to an optical fiber or fiber optic connector.
A common design approach is to attach the optical semiconductor device containing the light source to a TOSA lead frame or the photodiode to a ROSA lead frame. The anode and cathode of the optical semiconductor device are then connected to the lead frame via wire bonding processes. The lead frame and the optical semiconductor device may be encapsulated inside, for example, a clear mold compound via standard transfer molding process. The optical element, which is used to focus light, may be formed during the molding process and, thereby, directly integrated with the clear mold compound and positioned directly in front of an active region of the optical semiconductor device to improve coupling efficiency. The encapsulated TOSA or ROSA may be soldered to an electronics subassembly (ESA). The ESA may contain, for instance, a printed circuit board, a driver integrated circuit (IC), a receiver IC, and passive elements, such as resistors, capacitors, and inductors. The leads of the TOSA may be connected to the driver IC via conductive traces on the PCB, and the leads of the ROSA may be connected to the receiver IC via conductive traces on the PCB.
There are a number of disadvantages to these designs. The lead frame that is used to mount the light source and the photodiode is typically structurally weak and may be easily damaged during encapsulation. The coefficient of thermal expansion between the encapsulation compound and the metal lead frame may cause cracks and delamination may develop between the clear mold and the lead frame bonding surfaces, for example, during soldering of the leads to the ESA. The bond wire disadvantageously increases the overall thickness of the TOSA and the ROSA, and may increase yield loss due to bond wire breakage. Furthermore, the bond wires may partially obstruct light rays between the optics and the optical semiconductor device.
Thus, there remains a need in the art for improved designs for optical subassemblies used in opto-electronic assemblies.